1. Field of the Invention
The present invention disclosed herein relates to a method and apparatus for depositing a thin film, and more particularly, to an apparatus and method for forming a planar thin film using a plasma and ramping-down deposition processes.
2. Description of the Related Art
Chemical vapor deposition (CVD) is generally used to deposit a thin film on a wafer. An apparatus for forming the thin film on the wafer using the CVD process may be a single-type apparatus for processing a single wafer or a batch-type apparatus for simultaneously processing multiple wafers. An example of a batch-type apparatus is a CVD apparatus having a vertical tube type reaction furnace, which may include a reaction furnace having an outer tube and an inner tube. A boat disposed in the reaction furnace may receive a plurality of wafers. A heater may disposed outside of the reaction furnace. Gas required for the CVD process may be supplied from a nozzle and exhausted through an exhaust portion.
The concentration of the gas may be reduced with distance from the nozzle. This may result in the uneven layering of the thin films on the wafers. Furthermore, since the gas flow must enter the stack of wafers, the gas concentration, and resulting thin film layers, may be uneven between the edge and center of the wafers.
When an insulating thin film layer, e.g., a nitride layer, is deposited on a wafer using the described CVD apparatus, the insulating thin film layer may be uneven due to non-uniform reaction gas concentration. That is, the density and thickness of the insulating thin film layer may be uneven between the edge and center of the wafer. If the insulation layer is thick at the edge and thin at the center, the breakdown voltage (BV) at the edge of the wafer W will be greater than the BV at the center of the wafer. This may compromise electrical properties of the semiconductor and reduce yields.